Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $58.38   6.446%   $62.1432   $62.14   $62.15   $62.10  
  Purchase #2 $106.31   9.276%   $116.1713   $116.17   $116.15   $116.20  
  Purchase #3 $127.61   5.351%   $134.4384   $134.44   $134.45   $134.40  
  Purchase #4 $101.71   7.823%   $109.6668   $109.67   $109.65   $109.70  
  Purchase #5 $111.91   5.292%   $117.8323   $117.83   $117.85   $117.80  
  Purchase #6 $68.59   9.203%   $74.9023   $74.90   $74.90   $74.90  
  Purchase #7 $171.45   9.458%   $187.6657   $187.67   $187.65   $187.70  
  7 purchase totals = $745.96       $802.8200   $802.82   $802.80   $802.80